I've never been on a cruise before and need some advice on what sort of temperatures to dress for. The agency booking this group said the temps would be in the 80's. I don't want to get caught with only shorts and tees for daytime if it's likely to be in cooler.... I'm trying to plan ahead and not overpack too much and need all the advice I can get!

Karen:
What island are you visiting? Most Caribbean destinations will definitely be in the 80's in February....maybe even a little warmer. I always pack either a light jacket or sweater because it can be chilly inside the ship with air conditioning. Enjoy your first cruise!

I'll be on a 7 day HAL trip to St. Thomas, San Juan, and Half-Moon Cay. I planned on taking something light, sweater or jacket just in case I needed something...

Sounds like a perfect plan. You might need that sweater or light jacket in the mornings, or sometimes in the dining room, or even theater in the evenings! Don't waste space taking much more than that to keep warm. You won't need it.